Conventionally, as an engine such as a four-cycle engine for a vehicle, an engine including a turbocharger using an exhaust turbine driven by exhaust is known.
An exhaust system of the engine including the exhaust turbocharger is provided with a waste gate valve (a valve). The waste gate valve bypasses a portion of a passage that supplies engine exhaust to the exhaust turbine from the passage so as to open and close an exhaust bypass passage leading to an exhaust outlet passage. When a flow rate of exhaust is increased, that is, when an engine speed is high, the waste gate valve is opened. A portion of exhaust flowing toward the exhaust turbine is bypassed by opening of the waste gate valve. For this reason, excessive supply of exhaust to the exhaust turbine is restricted and an amount of supercharge (engine output) is suppressed within a proper range.
FIGS. 6A and 6B are views illustrating an exhaust turbine of an exhaust turbocharger equipped with a conventional valve. FIG. 6A is a front view of principal parts and FIG. 6B is a cross-sectional view of the principal parts.
In FIGS. 6A and 6B, reference numeral 1 designates a turbine casing of an exhaust turbine, reference numeral 2 designates a turbine provided within the turbine casing 1, and reference numeral 3 designates a waste gate valve. The waste gate valve 3 opens and closes an opening 5 provided upstream from an exhaust passage 4. The exhaust passage 4 communicates with an exhaust outlet passage 6 when the waste gate valve 3 is opened. Thus, exhaust supplied from an engine (not shown) via the exhaust passage 4 to the turbine 2 is introduced into the exhaust outlet passage 6 and bypasses the turbine 2.
The waste gate valve 3 includes a valve body 7, an arm 8, and a drive portion 9. The valve body 7 opens and closes the opening 5. When the valve is closed, the valve body 7 is pressed against a valve seat 5a so as to surround the opening 5. The arm 8 supports the valve body 7. The drive portion 9 rotates the arm 8 about a support point P to move the valve body 7 in a direction of intersecting the opening 5.
A specific configuration of the drive portion 9 will be omitted. The drive portion 9 uses an actuator or the like as a drive source which is not shown. When the speed of a basic engine is equal to or less than a predetermined speed (for example, 3000 rpm˜round/min), the drive portion 9 closes the valve body 7 through the arm 8. When the speed of the basic engine is equal to or greater than a predetermined speed, the drive portion 9 opens the valve body 7 through the arm 8 (for example, see PLT 1).